This invention relates generally to the field of control of antilock braking for vehicles, and in particular, to a system and method for vehicle stability enhancement control during vehicle operation.
Vehicle stability enhancement (VSE) has become more common on vehicles. VSE has been traditionally performed by applying brake pressure to one wheel, conventionally the front wheel on the outside of the turn if the vehicle is oversteering, and the rear wheel on the inside of the turn if the vehicle is understeering. VSE reduces vehicle spins and excessive understeer, reducing the difference between the driver""s requested direction and the actual vehicle direction. VSE uses various sensors to look at the difference between the driver""s requested direction and the yaw rate, and then manages individual wheel braking to bring the vehicle back toward the driver""s requested direction. However, in order to achieve the required corrective action with only one wheel, the brake pressure apply must be aggressive, which causes the vehicle pitch and roll to be apparent to the driver. At high vehicle speeds, it is possible to reach a point where corrective action applied to only one wheel may not provide enough yaw correction to stabilize the vehicle.
During maneuvers performed at or close to the limit of adhesion, vehicle lateral dynamics are strongly influenced by the surface coefficient of adhesion. In order to achieve satisfactory vehicular performance under all road conditions, a control algorithm should provide adaptation to the surface coefficient of adhesion.
Accordingly, it would be desirable to have a system and method of vehicle stability enhancement control that allows making VSE more effective at high speeds and making the corrective action more comfortable to the driver while attaining the necessary level of control and determining and applying an optimum amount of force for a given surface.
One aspect of the invention provides a method of vehicle stability enhancement control for determining a Delta Velocity of the vehicle, determining one of an understeer and an oversteer condition of the vehicle, applying a percentage of the Delta Velocity to an outside front and an outside rear wheel in the oversteer condition, and applying a percentage of the Delta Velocity to an inside front and an inside rear wheel in the understeer condition.
Another aspect of the invention provides a method for applying the Delta Velocity to a rear wheel during the oversteer condition using fluid pressure from a master cylinder when braking is occurring.
Still another aspect of the invention provides a method for applying the Delta Velocity to a front wheel during the understeer condition using fluid pressure from a master cylinder when braking is occurring.
Another aspect of the present invention provides a method for applying the Delta Velocity to a rear wheel during the oversteer condition using an isolated hydraulic circuit when braking is not occurring.
Another aspect of the present invention provides a method for applying the Delta Velocity to a front wheel during the understeer condition using an isolated hydraulic circuit when braking is not occurring.
The invention provides the foregoing and other features, and the advantages of the invention will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention and do not limit the scope of the invention, which is defined by the appended claims and equivalents thereof.